关于Android Service真正的完全详解

android service 的三种使用方法
原文链接：https://blog.csdn.net/javazejian/article/details/52709857

法一：onCreate()--onStartCommand--onDestroy
法二：binder onCreate-- onBinder -- onUnBinder -- onDestroy
法三：Messenger onCreate -- onBinder -- onUnBinder -- onDestory

法一：onCreate()--onStartCommand--onDestroy

<manifest ... >
...
<application ... >
    <service android:name=".service.SimpleService" />
    ...
</application>
</manifest>

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button startBtn;
    private Button stopBtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startBtn= (Button) findViewById(R.id.startService);
        stopBtn= (Button) findViewById(R.id.stopService);
        startBtn.setOnClickListener(this);
        assert stopBtn != null;
        stopBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        Intent it=new Intent(this, SimpleService.class);
        switch (v.getId()){
            case R.id.startService:
                startService(it);
                break;
            case R.id.stopService:
                stopService(it);
                break;
        }
    }
}  

public class SimpleService extends Service {

    /**
     * 绑定服务时才会调用
     * 必须要实现的方法  
     * @param intent
     * @return
     */
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    /**
     * 首次创建服务时，系统将调用此方法来执行一次性设置程序（在调用 onStartCommand() 或 onBind() 之前）。
     * 如果服务已在运行，则不会调用此方法。该方法只被调用一次
     */
    @Override
    public void onCreate() {
        System.out.println("onCreate invoke");
        super.onCreate();
    }

    /**
     * 每次通过startService()方法启动Service时都会被回调。
     * @param intent
     * @param flags
     * @param startId
     * @return
     */
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.println("onStartCommand invoke");
        return super.onStartCommand(intent, flags, startId);
    }

    /**
     * 服务销毁时的回调
     */
    @Override
    public void onDestroy() {
        System.out.println("onDestroy invoke");
        super.onDestroy();
    }
}

法二：onCreate-- onBinder -- onUnBinder -- onDestroy

public class LocalService extends Service{
    private final static String TAG = "wzj";
    private int count;
    private boolean quit;
    private Thread thread;
    private LocalBinder binder = new LocalBinder();

    /**
     * 创建Binder对象，返回给客户端即Activity使用，提供数据交换的接口
     */
    public class LocalBinder extends Binder {
        // 声明一个方法，getService。（提供给客户端调用）
        LocalService getService() {
            // 返回当前对象LocalService,这样我们就可在客户端端调用Service的公共方法了
            return LocalService.this;
        }
    }

    /**
     * 把Binder类返回给客户端
     */
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return binder;
    }


    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "Service is invoke Created");
        thread = new Thread(new Runnable() {
            @Override
            public void run() {
                // 每间隔一秒count加1 ，直到quit为true。
                while (!quit) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    count++;
                }
            }
        });
        thread.start();
    }

    /**
     * 公共方法
     * @return
     */
    public int getCount(){
        return count;
    }
    /**
     * 解除绑定时调用
     * @return
     */
     @Override
    public boolean onUnbind(Intent intent) {
        Log.i(TAG, "Service is invoke onUnbind");
        return super.onUnbind(intent);
    }

    @Override
    public void onDestroy() {
        Log.i(TAG, "Service is invoke Destroyed");
        this.quit = true;
        super.onDestroy();
    }
}

public class BindActivity extends Activity {
    protected static final String TAG = "wzj";
    Button btnBind;
    Button btnUnBind;
    Button btnGetDatas;
    /**
     * ServiceConnection代表与服务的连接，它只有两个方法，
     * onServiceConnected和onServiceDisconnected，
     * 前者是在操作者在连接一个服务成功时被调用，而后者是在服务崩溃或被杀死导致的连接中断时被调用
     */
    private ServiceConnection conn;
    private LocalService mService;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bind);
        btnBind = (Button) findViewById(R.id.BindService);
        btnUnBind = (Button) findViewById(R.id.unBindService);
        btnGetDatas = (Button) findViewById(R.id.getServiceDatas);
        //创建绑定对象
        final Intent intent = new Intent(this, LocalService.class);

        // 开启绑定
        btnBind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "绑定调用：bindService");
                //调用绑定方法
                bindService(intent, conn, Service.BIND_AUTO_CREATE);
            }
        });
        // 解除绑定
        btnUnBind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "解除绑定调用：unbindService");
                // 解除绑定
                if(mService!=null) {
                    mService = null;
                    unbindService(conn);
                }
            }
        });

        // 获取数据
        btnGetDatas.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (mService != null) {
                    // 通过绑定服务传递的Binder对象，获取Service暴露出来的数据

                    Log.d(TAG, "从服务端获取数据：" + mService.getCount());
                } else {

                    Log.d(TAG, "还没绑定呢，先绑定,无法从服务端获取数据");
                }
            }
        });


        conn = new ServiceConnection() {
            /**
             * 与服务器端交互的接口方法 绑定服务的时候被回调，在这个方法获取绑定Service传递过来的IBinder对象，
             * 通过这个IBinder对象，实现宿主和Service的交互。
             */
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                Log.d(TAG, "绑定成功调用：onServiceConnected");
                // 获取Binder
                LocalService.LocalBinder binder = (LocalService.LocalBinder) service;
                mService = binder.getService();
            }
            /**
             * 当取消绑定的时候被回调。但正常情况下是不被调用的，它的调用时机是当Service服务被意外销毁时，
             * 例如内存的资源不足时这个方法才被自动调用。
             */
            @Override
            public void onServiceDisconnected(ComponentName name) {
                mService=null;
            }
        };
    }
}

法三：Messenger
onCreate -- onBinder -- onUnBinder -- onDestory

public class ActivityMessenger extends Activity {
    /**
     * 与服务端交互的Messenger
     */
    Messenger mService = null;

    /** Flag indicating whether we have called bind on the service. */
    boolean mBound;

    /**
     * 实现与服务端链接的对象
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            /**
             * 通过服务端传递的IBinder对象,创建相应的Messenger
             * 通过该Messenger对象与服务端进行交互
             */
            mService = new Messenger(service);
            mBound = true;
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            mService = null;
            mBound = false;
        }
    };

    public void sayHello(View v) {
        if (!mBound) return;
        // 创建与服务交互的消息实体Message
        Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);
        try {
            //发送消息
            mService.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_messenager);
        Button bindService= (Button) findViewById(R.id.bindService);
        Button unbindService= (Button) findViewById(R.id.unbindService);
        Button sendMsg= (Button) findViewById(R.id.sendMsgToService);

        bindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("zj","onClick-->bindService");
                //当前Activity绑定服务端
                bindService(new Intent(ActivityMessenger.this, MessengerService.class), mConnection,
                        Context.BIND_AUTO_CREATE);
            }
        });

        //发送消息给服务端
        sendMsg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sayHello(v);
            }
        });


        unbindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Unbind from the service
                if (mBound) {
                    Log.d("zj","onClick-->unbindService");
                    unbindService(mConnection);
                    mBound = false;
                }
            }
        });
    }

}

public class MessengerService extends Service {

    /** Command to the service to display a message */
    static final int MSG_SAY_HELLO = 1;
    private static final String TAG ="wzj" ;

    /**
     * 用于接收从客户端传递过来的数据
     */
    class IncomingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SAY_HELLO:
                    Log.i(TAG, "thanks,Service had receiver message from client!");
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

    /**
     * 创建Messenger并传入Handler实例对象
     */
    final Messenger mMessenger = new Messenger(new IncomingHandler());

    /**
     * 当绑定Service时,该方法被调用,将通过mMessenger返回一个实现
     * IBinder接口的实例对象
     */
    @Override
    public IBinder onBind(Intent intent) {
        Log.i(TAG, "Service is invoke onBind");
        return mMessenger.getBinder();
    }
}